Anyone tried Biosyn in a rotary engine yet?

[dgeesaman]

I have a 3rd gen RX-7. These cars are famous for fuel dilution - I don't have any UOAs, but most owners run heavier oil such as 20w-50 just to counteract the fuel dilution.

Anyone tried the Biosyn with this application yet?

Also, I'm to understand that Biosyn will also lose viscosity as the fuel dilution builds up, but its anti-wear properties remain much more stable. So if I were to base a comparison, I should be looking at the wear metals for improvement moreso than measured viscosity, correct?

Dave

 

[d00df00d]

Hi Dave! I don't know if you remember me from the Maxima forums, but you rebuilt a transmission for me a while back and we actually had a conversation about BioSyn a few months ago.

As I understand, wear metal content is always the primary indicator of an oil's performance, and other measures -- viscosity, flash point, TAN, TBN, oxidation, nitration, etc. -- serve to indicate factors in that performance.

I also understand that BioSyn stands up to fuel dilution in three ways:

- It seals piston rings so less fuel sees the sump.
- It doesn't mix readily with fuel.
- Even when it does mix with fuel, fuel won't break it down.

What I definitely don't know is to what extent the aspects of RLI's chemistry that promote piston ring sealing are dependent on the metallurgy of a piston ring, and if that metallurgy differs significantly from that of an apex seal.

 

[BarkerMan]

Do a search on RI_RS4. There is a lot of info from a well informed owner that has worked with Dyson Analysis on a car that is a fuel dilution monster, the Audi 4.2 V8. You will get facts, numbers and qualified comments on BioSyn.

 

[dgeesaman]

Yes, Justin, of course I remember.

I guess the challenge for me is that 1) I only do 4-6k miles per year in my car, and 2) when draining oil, about 2 qt stays in the oil coolers/lines. So it's very difficult to get a complete oil change that will serve as a good UOA baseline.

In any case, apex seals are typically cast iron. Piston rings are quite a bit different metallurgically, but clearly iron wear particle count should be informative. I'm tempted to try it out and do some UOAs, but frankly turbo rotary owners have much bigger fish to fry than worrying about a little sliding wear.

Barkerman, to put it bluntly the 4.2 discussions are unreasonably large. I will continue pursuing the bookwork by digging through it, but I was hoping to stumble across a fellow rotary nut who might provide an executive summary.

I also hope it burns nice and clean. In spite of Mazda's formal stance against using synthetic oils, the fact is that modern synthetics burn very cleanly and definitely reduce wear in rotary engines. As long as Biosyn doesn't slide back in that regard it sounds like a legitimate improvement over the state of the art.

Dave

 

[d00df00d]

Even the 5w-40 HD oil (with the "kitchen sink" additive pack) is being billed as being extremely eco-friendly and usable where an API SM oil is specced. That makes me very optimistic that the oil burns cleanly.

As for the oil drain issue, would there be a way to suck more oil out with a pump or something?

 

[dgeesaman]

Well I think I have to disconnect the oil cooler lines to drain them, and that's assuming the lines run from the bottom of the coolers. I've never done it because I've heard it's a major PITA.

 

[gtx510]

FD oil lines are easy to disconnect. Just use a flatblade screwdriver to pry the retaining clip out and the fitting pulls apart. Don't lose the clip.

I've been wonder how fuel gets into the oil, it's not like it can go down the bores. It'd have to push past the side seals and oil control rings?

 

[san123chez]

This may be a little off topic, but if you're looking for a rotary specific oil, idemitsu has a couple of weights that are designed to work well with rotary engines. Just another avenue you might want to look down.

 

[gtx510]

Idemitsu got mentioned few times in the other rotary thread.
https://bobistheoilguy.com/forums/threads/1st-generation-rx-7-oil-discussion-rotary-engine.82573/

 

[dgeesaman]

Idemitsu is just oil like the others. Biosyn is the only product in my mind that's actually doing something a little different. If I can go down one viscosity weight without increasing wear I'll get better cooling. That's important.

Dave

 

[d00df00d]

Interesting:

http://www.rotorsportsracing.com/performancetuning/idemitsu.htm

Is that it?

The list of purported features reads very similarly to BioSyn's: low friction and wear, improved combustion chamber sealing, no coking, and clean burning.

The only certain difference I can see is that Idemitsu uses a lot of moly, whereas BioSyn uses none. However, I wouldn't worry about that since BioSyn's wear protection and friction reduction abilities are not really in dispute.

I find it interesting that Idemitsu makes a strong point of anti-foaming properties. I wonder if that's just marketing speak (all oils have some anti-foaming additives) or if that property really is particularly important in a rotary.

 

[dgeesaman]

I've never heard of anti-foaming to be a major consideration. Fuel dilution is the biggest topic.

I'm tempted to do a complete drain and UOA at 1k, 2k, and 3k. I plan to compare Mobil1 (my current oil), Biosyn, and maybe Idemitsu (considered a gold standard by some rotary nuts).

Unfortunately I don't do lots of miles so results would be next year at the earliest.

Dave

 

[gtx510]

Isn't a rotary oil pump different than most oil pumps?
But I've never heard of rotaries having foaming problems with regular engine oils.
Do this page work for you guys?
http://www.rotaryengineillustrated.com/how-a-rotary-engine-works/lubrication-oil-system.html

You might also try looking for a low-SAPS synthetic oil and see how that UOA looks?

Where does the fuel dilution come from? How does the fuel get into the oil?

 

[dgeesaman]

I don't know where exactly the fuel dilution comes in. But the oil definitely smells of gas after 2-3k miles when I do my change.

I tried disconnecting the oil cooler lines as you said but very little additional oil drained out. So there remains 1.7 qts inside the engine no matter what I do. I guess I could change the oil when it's scorching hot but that doesn't seem like a wise thing to do.

What I may do is a very short drain/replace between oil type changes and use that oil again in my more pedestrian vehicles. Considering that Idemitsu and RLI cost over $40/oil change, I won't be throwing it away.

Dave

 

[Jax_RX8]

FYI - The fuel dilution comes from the very rich fuel mixture that the rotary must run in order to operate properly.

The rotary's Air/Fuel ratio ranges from 10.5-13.5 to 1, depending on load - much more than the typical piston engine's 14.7 to 1 (Stoch__) and leaner.

This leaves a lot more unburned fuel than a piston engine that blows by the oil seals and gets into the oil. This is also why rotary's are known to be carbon monsters - increasing the need for regular fuel cleaners (hopefully lubricious ones like FP Plus or MMO) to clean it all out without killing the oil film.

Even if you used RLI, which handles fuel dilution well, you really are better off with a rotary just biting the bullet and changing the oil every 2500 miles (3750 max).

 

[dgeesaman]

I'm not interested in extending OLIs.

I'm interested in an oil that is more viscosity-stable with fuel dilution, and to see if going thinner is acceptable from a wear point of view. If I can run one or two grades thinner than 15w-50 I'll improve cooling on the track and maybe gain a little HP.

Dave

 

[Jax_RX8]

I See - with that in mind, the most critical thing you need to do is get a good reading on your oil temps on the track - then correlate this to your preferred cst at this temp, and then pick you oil viscosity to match them up.

Of course, going thinner may not necessarily mean less protection, expecially if you go with say, a 10W40 Redline as it claims to have oil films equivalent to one viscosity rating higher for other oils. RLI is developing quite a reputation as well for not being effected by high fuel dilution. Also PP is also showing pretty good wear numbers as well.

Just some thoughts to consider.

 

[d00df00d]

This is not my area of expertise, but I would have thought it would run A/F ratios between 10.5 and 13.5 just because it's a high boost AND high RPM application. Piston engines do try to get a stoichiometric A/F in closed loop mode, but when you open the throttle and bring the revs up, even NA engines end up between 13 and 14. It's not unheard of for turbo piston engines to go much lower than that to keep combustion chamber temps down and have a margin of safety against pre-detonation; these effects would be even more important if the engine also had a high redline. Under such conditions, I was under the impression that an A/F ratio of 10 or 11 would not be unheard of.

Am I wrong? If so, what is it about a rotary engine that requires richer running?

 

[dgeesaman]

Justin,

It's a multi-pronged answer. I don't think RPM has much if anything to do with it: it's more a matter of hedging against heat and risk of detonation.

During startup, the FD runs extra rich. Possibly it's to *increase* temps in the exhaust (afterburn?!) and kick-start the catalytic reactions. Or maybe it's just rich for smooth starting and driveability reasons.

The main issue with a turbo rotary is that detonation or preignition is just that much more destructive. On a boosted piston engine it puts excess stress and starts pitting the surfaces. In any case, piston engines have some level of tolerance. In a rotary, either event will *break* the seals, likely on the first such combustion event. Keeping chamber temps down and rich both help avoid preignition and detonation.

As well, the combustion temps tend to be higher. So lower combustion temps is a lower cooling system load, which improves seal longevity and reduces the size/weight of accessory cooling systems. Plus, Mazda only recommended premium fuel, which means it's supposed to be safe to run on 87 octane. (No sane FD owner does that, considering the risks). So while the Mazda engineers have never commented on it, I suspect it's tuned rich for all of those reasons.

Good aftermarket tuners will go a bit closer to stoich and definitely leaner in startup than the stock ECU. Of course, they have the luxury of tuning for a specific fuel, specific boost level, frequent plug changes, and they have the benefit of using EGT and wideband to *know* what combustion looks like in that specific car. Stock ECUs will never be programmed with that level of certainty.

Back to the original topic, I got word that the large bolt-type fitting on the oil coolers is the thermostat that is preventing the oil from draining from them. I'm also told that using an air compressor can help blast pooled oil out of the engine and into the oil pan, which is rumored to be at least a cup or two. So the 100% oil drain theory remains plausible for now.

Dave

 

[d00df00d]

Thanks for clearing that up about tuning.

Here's a question for you: What is the typical failure mode for the apex seal? Is it just friction?